1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a return path section.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a coil and a main pole. The main pole has an end face located in a medium facing surface facing a recording medium. The coil produces a magnetic field corresponding to data to be written on the recording medium. The main pole allows a magnetic flux corresponding to the magnetic field produced by the coil to pass, and produces a write magnetic field from its end face.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of a recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium.
Here, the side of positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks in the neighborhood of a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. Unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording density, it is necessary to prevent unwanted erasure.
In order to prevent unwanted erasure induced by the skew and achieve higher recording density, it is effective to provide a return path section that has an end face located in the vicinity of the end face of the main pole in the medium facing surface, as disclosed in, for example, U.S. Pat. No. 6,954,340 B2.
The return path section is magnetically connected to a portion of the main pole away from the medium facing surface so that one or more spaces are formed between the return path section and the main pole. A coil is provided to pass through the one or more spaces. The return path section has the function of capturing from the end face of the return path section a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of a recording medium, and thereby preventing the magnetic flux from reaching the recording medium. The return path section further has the function of capturing from the end face of the return path section a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium, and allowing the magnetic flux to flow back to the main pole. A magnetic head having such a return path section allows the prevention of unwanted erasure and provides a further improvement in recording density.
In the magnetic head disclosed in U.S. Pat. No. 6,954,340 B2, the end face of the return path section is exposed over a large area in the medium facing surface. In this case, part of the magnetic flux captured into the return path section from a portion of the end face of the return path section located in the vicinity of the end face of the main pole may leak from another portion of the end face of the return path section toward the recording medium. This may result in the occurrence of unwanted erasure.
To avoid the above-described problem, reducing the return path section in dimension in the track width direction, for example, is conceivable. Doing so, however, results in a reduction in the volume of the return path section, and thus makes the return path section prone to flux saturation. As a result, there arises a problem that magnetic flux leaks from the end face of the return path section toward the recording medium to cause unwanted erasure.